Design patterns

A design pattern is a formal way of documenting a solution to a design problem in a particular field of expertise. The idea was introduced by the architect Christopher Alexander in the field of architecture, and has been adapted for various other disciplines, including computer science.

An organized collection of design patterns that relate to a particular field is called a pattern language.

Defining "good" solutions

A pattern must explain why a particular situation causes problems, and why the proposed solution is considered a good one.

Alexander describes common design problems as arising from "conflicting forces" -- such as the conflict between wanting a room to be sunny and wanting it not to overheat on summer afternoons. A pattern would not tell the designer how many windows to put in the room; instead, it would propose a set of values to guide the designer toward a decision that is best for their particular application. Alexander, for example, suggests that enough windows should be included to direct light all around the room. He considers this a good solution because he believes it increases the enjoyment of the room by its occupants. Other authors might come to different conclusions, if they place higher value on heating costs, or material costs. These values, used by the pattern's author to determine which solution is "best", must also be documented within the pattern.

Design problems in a context

A pattern must also explain when it is applicable. Since two houses may be very different from each other, a design pattern for houses must be broad enough to apply to both of them, but not so vague that it doesn't help the designer make decisions.

The range of situations in which a pattern can be used is called its context. Some examples might be "all houses", "all two-story houses", or "all places where people spend time." The context must be documented within the pattern.

For instance, in Alexander's work, bus stops and waiting rooms in a surgery are both part of the context for the pattern "A PLACE TO WAIT."

Domain-specific articles

• Pattern (architecture), a way of capturing and communicating design ideas in architecture.
• Design pattern (computer science), a standard solution to common problems in software design.
• Architectural pattern (computer science), a standard solution to architectural problems in software engineering.
• Interaction design pattern, used in interaction design / HCI.
• Pedagogical patterns, documenting good practices in teaching.

Book titles

• A Pattern Language by Christopher Alexander, with patterns for the design of towns and buildings (architecture).
• Design Patterns ("Gang-of-four book") by Erich Gamma et al, with patterns for object-oriented programming (software engineering).
• Designing Interfaces by Jenifer Tidwell, with patterns for interaction design
• head first design patterns by Eric Freeman and Elisabeth Freeman, a book that explains design patterns in an interesting and simple way

See also

• Style guide, repeatable graphic design elements and styles.

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

Article keywords: head first design pattern,